The skin is an important secretory and excretory organ of the body. Water is transpired through the skin. It also serves to excrete certain glycoid and nitrogenous wastes via apocrine perspiration. In addition hair grows from the skin and sebum is secreted.
Sebum is a holocrine secretion of the sebaceous glands. It is a thick semifluid secretion composed of fatty material and epithelial debris from the cells of the malpighian layer. The sebaceous glands are scattered over the surface of the skin. They lie in the derma layer of the skin and generally their excretory duct opens into the neck of a hair sac.
The largest sebaceous glands are on and around the nose, forehead and the ears. Thus the largest quantity of sebum is secreted in the most visible areas of the person. Given present fashion, this oily residue on the skin surface presents a cosmetic problem.
Sebum itself results from the normal destruction of the epithelial cells followed by regeneration of the numerous epithelial elements. In the body of the sebaceous gland, mitosis is numerous in the cells close to the walls of the excretory ducts along the hair shaft wherein the new cells form replacements and move into the secretory regions. Thus the base of the hair, where the sebum emerges from the skin, is coated with oils and a proteinaceous mixture composed of exfoliated cellular debris. This, too, presents a cosmetic problem which is solved by shampooing regularly. Much of dandruff, decried in the advertisements as a social disease, is this exfoliation of the epithelial cells.
While anatomically sebum is the combined excretion of the dead cellular matter, the fatty oils and water, the term most commonly refers to the fatty-components. The cellular matter usually comprises 20 to 40 weight percent of the excretion of the sebaceous glands. The broad variation results from age and health differentials. The amount of water in sebum is also subject to variation due to metabolism, thermal controls and the sterol content of the fatty components.
In addition, small amounts of complex sugars from the decomposition of glycoprotein are present. These are oligomers of glycogen. Cerumen contains much of such sugars.
The composition of human sebum is subject to much variation between individuals and between areas of the body as well as a result of dietary variations. Vitamin A and Vitamin E have been reported to change the proportions within the composition of the fatty components of sebum. A representative analysis of the fatty components of sebum is represented in Table I below:
TABLE I ______________________________________ Composition of Human Sebum ______________________________________ Free fatty acids (saturated) 14.3% Free fatty acids (unsaturated) 14.0 Triglycerides 32.5 Waxes (excluding cholesterol esters) 14.0 Free cholesterol 2.0 Cholesterol esters 2.1 Other sterols 0.4 Squalene (C.sub.30 H.sub.50) 5.5 Paraffins (branched chains) 8.1 C.sub.14 to C.sub.24 alkane-diols 2.0 Not specified 5.1 ______________________________________
Generally it is desired to remove accumulated total sebum from the skin and hair. The use of soaps and other detergents as surfactant materials generally emulsifies the fatty materials in a more or less satisfactory manner. During this emulsification the cellular debris is also loosened and upon rinsing the skin and hair is cleansed. However the use of soaps or detergents has a drying effect upon the skin surface. The emollience of the skin is removed together with the normal moisture. The skin and hair are thus excessively dried leading to separate complicating cosmetic problems.